I recently bought a 2006 BMW 330xi from Pace BMW.  When I drove the car home that Friday I heard a scraping noise coming from the back.  I brought it back the following week and they fixed the rear brakes.  They said it was a bad sensor and pad.  Well by the time I got home it happened again.  So I took it back again and this time they found it.  It was a baffle in the muffler that came loose.  Replaced the muffler, window switch and grab handle all under warranty.  The best part was I drove a 335xi for 3 days while they order the parts for my car.